Turbo machines, such as gas turbine engines, may include an actuation system coupled to a plurality of stages of vane airfoils via a synchronization or unison ring. The actuation system operates along a linear direction to rotate an angle of the plurality of stages of vanes simultaneously. The actuation system generally moves according to a predetermined schedule based on changes in engine operating mode, such as to improve operability or performance of the turbo machine at various operating modes.
Known variable vane assemblies include an actuation system coupled to a plurality of unison rings corresponding to a plurality of axially separated stages of the turbo machine. Each unison ring is coupled to the plurality of vanes at each stage such that linear movement of the actuation system results in rotation of the vanes at each stage.
However, coupling the actuation system to the plurality of vanes at via the unison rings results in uniform movement of all stages of variable vanes. For example, the kinematics relationship between the actuation system and the motion of the variable vanes is a continuous uniform function (e.g. from linear to sinusoidal curvature), which does not enable localized and abrupt angular orientation variations.
This therefore limits the extent to which the actuation system and variable vanes may improve operability or performance of the turbo machine. Additionally, the uniform movement of all stages may adversely affect turbo machine operability or performance by adversely adjusting a first stage to positively adjust a second stage, or vice versa.
As such, there is a need for a variable vane system for a turbo machine that improves operability or performance of the turbo machine. Additionally, or alternatively, there is a need for a variable vane system that mitigates adverse effects due to changes at a first stage relative to changes at a second stage.